In the murine model, a latent CMV infaction may be produced 2 to 3 months after infection. The spleen cells show no virus, but produce CMV after co-cultivation on both syngeneic and allogeneic fibroblasts. Such mice will activate when injected with cyclophosphamide or azathioprine. Spleen cells may also be activated by transfer to syngeneic recipients and allogeneic (C57BL) recipients treated with cyclophosphamide. We are studying the requirements needed for co-cultivation of T and B lymphocytes to express CMV infection.